Say you have 200 ft of 6" SS steam pipe at 350 deg F would you add expansion loops to control the movement or put an anchor in the middle and let the pipe grow out in each direction? I've typically used expansion loops but some clients don't want to spend the extra money for loops if they're not needed. If the desgner says that say a 4.5" movement at the end of the run doesn't create a problem, is a loop really required?

The answer to your question rest in the branch lines from the main 6" header.
What are these branch lines (purpose & function)?
What is the size of each?
Where are they located along the main header?
How long are each branch from the main header to the first restriction to lateral movement?
How much movement would you have at each branch under each condition (w/loop and w/middle anchor)?

Check your header out each way and then select the best solution for your project.

4.5" displacement would not create a problem? perhaps in your aplication, but do you have a company standard of maximum pipe thermal displacement? For that long in my experience with steam lines in piperack 100ft to 114ft needs a loop or expansion joint perhaps...

Work with your Senior engineer.

Regards!

As per previous post, check your client’s flexibility standard or your company’s.
Usually clients accept/reject elimination of expansion loops based on more “serious” reasons (steam hammer!?) and cost comes in secondary; however, if you exceed the maximum allowed displacement, always request a formal deviation from the qualifying standard. Check the MOC (Management of Change) procedure and document properly.

better to avoid unnecessary expansion loops. placing anchor in between the 200ft should be fine. displacements of 2-3" at the ends could be easily absorbed at the unit piping.